1. Field of the Invention
The present invention relates to a video projector that projects and displays a picture on a screen based on an input video signal, and more specifically, it relates to a video projector capable of adjusting the size and position of a projected picture, and a method for shifting the projected picture.
2. Description of the Related Art
Conventionally, in order to display a picture created with a computer on a display device included in a video projector such as a liquid crystal projector, it is necessary to generate a video signal corresponding to the resolution of the display device, and supply it to the display device.
Japanese Unexamined Patent Application Publication No. 2003-84738, for example, discloses an apparatus that can perform display regardless of the resolution of the input video signal. The apparatus measures the frequency of the synchronizing signals in the input video signal; determines the resolution of the video signal based on the measured frequency; and performs video scaling, that is to say, changes (scales) the determined resolution of the video signal so as to agree to the resolution of the display device, thus enabling to display it on the display device.
Such a video projector includes a video-signal processing unit for changing the input analog video signal to a digital video signal; a scaler unit for scaling the number of pixels of the digital video signal to the number of pixels of the display device; a display-device drive unit for making the display device display a picture based on the digital video signal; a display device, such as a liquid crystal panel, functioning as a light valve; a lamp for emitting light to the display device; and a projection lens for projecting the picture displayed on the display device onto a screen.
In the case where the display device is a transmissive panel such as a liquid crystal panel, the light emitted from the lamp is transmitted by the display device, is refracted by the projection lens, and forms a projection image on the screen. In the case where the display device is a reflective panel such as a DMD (trademark), the light emitted from the lamp is reflected by the display device, is refracted by the projection lens, and forms a projection image on the screen. DMD (trademark) is an abbreviation of digital micromirror device, and is used in DLP light processing technology. DLP (trademark) is an abbreviation of digital light processing.
If the projection lens is provided with a mechanism for shifting the lens in the direction of the axis of projection, an “optical zooming operation”, which adjusts the size of the picture projected on the screen, can be performed.
If the projection lens is provided with a mechanism for shifting the lens in the direction perpendicular to the axis of projection, a “lens shifting operation”, which adjusts the position of the picture projected on the screen, can be performed.
There are two modes of use for a video projector, that is to say, permanent installation in a room with a fixed screen and temporary installation in various places. Especially in the case of the temporary installation, it is preferable to expand the range of choice for installation places, that is to say, it is preferable that the video projector project a picture on a screen (or a wall used as a screen) regardless of the size, position, and distance of the screen.
As described above, the optical zooming operation adjusts the size of the picture projected on the screen; and the lens shifting operation adjusts the position of the picture projected on the screen. If the video projector has the mechanisms for the optical zooming and shifting operations, the range of choice for installation places is expanded.
However, since the lens shifting mechanisms are expensive, there is a need for a method for adjusting the size and position of the projected picture in another way.